A predominant method for the synthesis of colloidal quantum dots involves reactions done in high boiling solvents, such as trioctylphosphine oxide (TOPO), trioctylphosphine (TOP), aliphatic phosphonic or carboxylic acids, and aliphatic amine species. The ligand capping groups on the surface of the quantum dots are, therefore, believed to be a statistical distribution of TOPO, TOP, acid, and amine. Throughout the quantum dot literature, in order to affect surface chemistry changes on a particular quantum dot sample (e.g. making water-soluble quantum dots), typical procedures involve cap exchange reactions, whereby already synthesized quantum dots (core or core-shell) are placed in a solution of another ligand and heated for an extended period of time in order to drive off the existing ligands and replace them with the alternate species. These procedures can be detrimental to maintaining the optical properties of the quantum dots and often result in drastically reduced emission efficiencies and stability.
Alternative techniques utilize self-assembled micelles that surround and inter-digitate with the native quantum dot surface ligands. The drawback of these methods include the requirement for polar solvent environments to generate the encapsulating micelle, and thus limiting the technique to aqueous based applications, such as biological tagging and imaging.
Thus, there remains a need for a semiconductor nanocrystal including functionalized ligands that are compatible with an organic based solvent system, and methods for preparing same.